perf probe: Show accessible local variables

Add -V (--vars) option for listing accessible local variables at given probe
point. This will help finding which local variables are available for event
arguments.

e.g.)
 # perf probe -V call_timer_fn:23
 Available variables at call_timer_fn:23
         @<run_timer_softirq+345>
                 function_type*  fn
                 int     preempt_count
                 long unsigned int       data
                 struct list_head        work_list
                 struct list_head*       head
                 struct timer_list*      timer
                 struct tvec_base*       base

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20101021101323.3542.40282.stgit@ltc236.sdl.hitachi.co.jp>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 317 insertions, 95 deletions

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index c6fe80ebb262..986027fa495f 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -172,8 +172,8 @@ static Dwarf_Die *die_get_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
                 return NULL;
 }
 
-/* Get type die, but skip qualifiers and typedef */
-static Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
+/* Get a type die, but skip qualifiers */
+static Dwarf_Die *__die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
 {
         int tag;
 
@@ -185,8 +185,17 @@ static Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
         } while (tag == DW_TAG_const_type ||
                  tag == DW_TAG_restrict_type ||
                  tag == DW_TAG_volatile_type ||
-                 tag == DW_TAG_shared_type ||
-                 tag == DW_TAG_typedef);
+                 tag == DW_TAG_shared_type);
+
+        return vr_die;
+}
+
+/* Get a type die, but skip qualifiers and typedef */
+static Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
+{
+        do {
+                vr_die = __die_get_real_type(vr_die, die_mem);
+        } while (vr_die && dwarf_tag(vr_die) == DW_TAG_typedef);
 
         return vr_die;
 }
@@ -380,6 +389,60 @@ static Dwarf_Die *die_find_member(Dwarf_Die *st_die, const char *name,
                               die_mem);
 }
 
+/* Get the name of given variable DIE */
+static int die_get_typename(Dwarf_Die *vr_die, char *buf, int len)
+{
+        Dwarf_Die type;
+        int tag, ret, ret2;
+        const char *tmp = "";
+
+        if (__die_get_real_type(vr_die, &type) == NULL)
+                return -ENOENT;
+
+        tag = dwarf_tag(&type);
+        if (tag == DW_TAG_array_type || tag == DW_TAG_pointer_type)
+                tmp = "*";
+        else if (tag == DW_TAG_subroutine_type) {
+                /* Function pointer */
+                ret = snprintf(buf, len, "(function_type)");
+                return (ret >= len) ? -E2BIG : ret;
+        } else {
+                if (!dwarf_diename(&type))
+                        return -ENOENT;
+                if (tag == DW_TAG_union_type)
+                        tmp = "union ";
+                else if (tag == DW_TAG_structure_type)
+                        tmp = "struct ";
+                /* Write a base name */
+                ret = snprintf(buf, len, "%s%s", tmp, dwarf_diename(&type));
+                return (ret >= len) ? -E2BIG : ret;
+        }
+        ret = die_get_typename(&type, buf, len);
+        if (ret > 0) {
+                ret2 = snprintf(buf + ret, len - ret, "%s", tmp);
+                ret = (ret2 >= len - ret) ? -E2BIG : ret2 + ret;
+        }
+        return ret;
+}
+
+/* Get the name and type of given variable DIE, stored as "type\tname" */
+static int die_get_varname(Dwarf_Die *vr_die, char *buf, int len)
+{
+        int ret, ret2;
+
+        ret = die_get_typename(vr_die, buf, len);
+        if (ret < 0) {
+                pr_debug("Failed to get type, make it unknown.\n");
+                ret = snprintf(buf, len, "(unknown_type)");
+        }
+        if (ret > 0) {
+                ret2 = snprintf(buf + ret, len - ret, "\t%s",
+                                dwarf_diename(vr_die));
+                ret = (ret2 >= len - ret) ? -E2BIG : ret2 + ret;
+        }
+        return ret;
+}
+
 /*
  * Probe finder related functions
  */
@@ -393,8 +456,13 @@ static struct probe_trace_arg_ref *alloc_trace_arg_ref(long offs)
         return ref;
 }
 
-/* Show a location */
-static int convert_variable_location(Dwarf_Die *vr_die, struct probe_finder *pf)
+/*
+ * Convert a location into trace_arg.
+ * If tvar == NULL, this just checks variable can be converted.
+ */
+static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
+                                     Dwarf_Op *fb_ops,
+                                     struct probe_trace_arg *tvar)
 {
         Dwarf_Attribute attr;
         Dwarf_Op *op;
@@ -403,7 +471,6 @@ static int convert_variable_location(Dwarf_Die *vr_die, struct probe_finder *pf)
         Dwarf_Word offs = 0;
         bool ref = false;
         const char *regs;
-        struct probe_trace_arg *tvar = pf->tvar;
         int ret;
 
         if (dwarf_attr(vr_die, DW_AT_external, &attr) != NULL)
@@ -411,16 +478,16 @@ static int convert_variable_location(Dwarf_Die *vr_die, struct probe_finder *pf)
 
         /* TODO: handle more than 1 exprs */
         if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL ||
-            dwarf_getlocation_addr(&attr, pf->addr, &op, &nops, 1) <= 0 ||
+            dwarf_getlocation_addr(&attr, addr, &op, &nops, 1) <= 0 ||
             nops == 0) {
                 /* TODO: Support const_value */
-                pr_err("Failed to find the location of %s at this address.\n"
-                       " Perhaps, it has been optimized out.\n", pf->pvar->var);
                 return -ENOENT;
         }
 
         if (op->atom == DW_OP_addr) {
 static_var:
+                if (!tvar)
+                        return 0;
                 /* Static variables on memory (not stack), make @varname */
                 ret = strlen(dwarf_diename(vr_die));
                 tvar->value = zalloc(ret + 2);
@@ -435,14 +502,11 @@ static_var:
 
         /* If this is based on frame buffer, set the offset */
         if (op->atom == DW_OP_fbreg) {
-                if (pf->fb_ops == NULL) {
-                        pr_warning("The attribute of frame base is not "
-                                   "supported.\n");
+                if (fb_ops == NULL)
                         return -ENOTSUP;
-                }
                 ref = true;
                 offs = op->number;
-                op = &pf->fb_ops[0];
+                op = &fb_ops[0];
         }
 
         if (op->atom >= DW_OP_breg0 && op->atom <= DW_OP_breg31) {
@@ -458,13 +522,18 @@ static_var:
         } else if (op->atom == DW_OP_regx) {
                 regn = op->number;
         } else {
-                pr_warning("DW_OP %x is not supported.\n", op->atom);
+                pr_debug("DW_OP %x is not supported.\n", op->atom);
                 return -ENOTSUP;
         }
 
+        if (!tvar)
+                return 0;
+
         regs = get_arch_regstr(regn);
         if (!regs) {
-                pr_warning("Mapping for DWARF register number %u missing on this architecture.", regn);
+                /* This should be a bug in DWARF or this tool */
+                pr_warning("Mapping for DWARF register number %u "
+                           "missing on this architecture.", regn);
                 return -ERANGE;
         }
 
@@ -689,8 +758,14 @@ static int convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)
         pr_debug("Converting variable %s into trace event.\n",
                  dwarf_diename(vr_die));
 
-        ret = convert_variable_location(vr_die, pf);
-        if (ret == 0 && pf->pvar->field) {
+        ret = convert_variable_location(vr_die, pf->addr, pf->fb_ops,
+                                        pf->tvar);
+        if (ret == -ENOENT)
+                pr_err("Failed to find the location of %s at this address.\n"
+                       " Perhaps, it has been optimized out.\n", pf->pvar->var);
+        else if (ret == -ENOTSUP)
+                pr_err("Sorry, we don't support this variable location yet.\n");
+        else if (pf->pvar->field) {
                 ret = convert_variable_fields(vr_die, pf->pvar->var,
                                               pf->pvar->field, &pf->tvar->ref,
                                               &die_mem);
@@ -772,34 +847,12 @@ found:
         return ret;
 }
 
-/* Show a probe point to output buffer */
-static int convert_probe_point(Dwarf_Die *sp_die, struct probe_finder *pf)
+/* Convert subprogram DIE to trace point */
+static int convert_to_trace_point(Dwarf_Die *sp_die, Dwarf_Addr paddr,
+                                  bool retprobe, struct probe_trace_point *tp)
 {
-        struct probe_trace_event *tev;
         Dwarf_Addr eaddr;
-        Dwarf_Die die_mem;
         const char *name;
-        int ret, i;
-        Dwarf_Attribute fb_attr;
-        size_t nops;
-
-        if (pf->ntevs == pf->max_tevs) {
-                pr_warning("Too many( > %d) probe point found.\n",
-                           pf->max_tevs);
-                return -ERANGE;
-        }
-        tev = &pf->tevs[pf->ntevs++];
-
-        /* If no real subprogram, find a real one */
-        if (!sp_die || dwarf_tag(sp_die) != DW_TAG_subprogram) {
-                sp_die = die_find_real_subprogram(&pf->cu_die,
-                                                 pf->addr, &die_mem);
-                if (!sp_die) {
-                        pr_warning("Failed to find probe point in any "
-                                   "functions.\n");
-                        return -ENOENT;
-                }
-        }
 
         /* Copy the name of probe point */
         name = dwarf_diename(sp_die);
@@ -809,26 +862,45 @@ static int convert_probe_point(Dwarf_Die *sp_die, struct probe_finder *pf)
                                    dwarf_diename(sp_die));
                         return -ENOENT;
                 }
-                tev->point.symbol = strdup(name);
-                if (tev->point.symbol == NULL)
+                tp->symbol = strdup(name);
+                if (tp->symbol == NULL)
                         return -ENOMEM;
-                tev->point.offset = (unsigned long)(pf->addr - eaddr);
+                tp->offset = (unsigned long)(paddr - eaddr);
         } else
                 /* This function has no name. */
-                tev->point.offset = (unsigned long)pf->addr;
+                tp->offset = (unsigned long)paddr;
 
         /* Return probe must be on the head of a subprogram */
-        if (pf->pev->point.retprobe) {
-                if (tev->point.offset != 0) {
+        if (retprobe) {
+                if (eaddr != paddr) {
                         pr_warning("Return probe must be on the head of"
                                    " a real function\n");
                         return -EINVAL;
                 }
-                tev->point.retprobe = true;
+                tp->retprobe = true;
         }
 
-        pr_debug("Probe point found: %s+%lu\n", tev->point.symbol,
-                 tev->point.offset);
+        return 0;
+}
+
+/* Call probe_finder callback with real subprogram DIE */
+static int call_probe_finder(Dwarf_Die *sp_die, struct probe_finder *pf)
+{
+        Dwarf_Die die_mem;
+        Dwarf_Attribute fb_attr;
+        size_t nops;
+        int ret;
+
+        /* If no real subprogram, find a real one */
+        if (!sp_die || dwarf_tag(sp_die) != DW_TAG_subprogram) {
+                sp_die = die_find_real_subprogram(&pf->cu_die,
+                                                  pf->addr, &die_mem);
+                if (!sp_die) {
+                        pr_warning("Failed to find probe point in any "
+                                   "functions.\n");
+                        return -ENOENT;
+                }
+        }
 
         /* Get the frame base attribute/ops */
         dwarf_attr(sp_die, DW_AT_frame_base, &fb_attr);
@@ -848,22 +920,13 @@ static int convert_probe_point(Dwarf_Die *sp_die, struct probe_finder *pf)
 #endif
         }
 
-        /* Find each argument */
-        tev->nargs = pf->pev->nargs;
-        tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
-        if (tev->args == NULL)
-                return -ENOMEM;
-        for (i = 0; i < pf->pev->nargs; i++) {
-                pf->pvar = &pf->pev->args[i];
-                pf->tvar = &tev->args[i];
-                ret = find_variable(sp_die, pf);
-                if (ret != 0)
-                        return ret;
-        }
+        /* Call finder's callback handler */
+        ret = pf->callback(sp_die, pf);
 
         /* *pf->fb_ops will be cached in libdw. Don't free it. */
         pf->fb_ops = NULL;
-        return 0;
+
+        return ret;
 }
 
 /* Find probe point from its line number */
@@ -899,7 +962,7 @@ static int find_probe_point_by_line(struct probe_finder *pf)
                          (int)i, lineno, (uintmax_t)addr);
                 pf->addr = addr;
 
-                ret = convert_probe_point(NULL, pf);
+                ret = call_probe_finder(NULL, pf);
                 /* Continuing, because target line might be inlined. */
         }
         return ret;
@@ -1012,7 +1075,7 @@ static int find_probe_point_lazy(Dwarf_Die *sp_die, struct probe_finder *pf)
                          (int)i, lineno, (unsigned long long)addr);
                 pf->addr = addr;
 
-                ret = convert_probe_point(sp_die, pf);
+                ret = call_probe_finder(sp_die, pf);
                 /* Continuing, because target line might be inlined. */
         }
         /* TODO: deallocate lines, but how? */
@@ -1047,7 +1110,7 @@ static int probe_point_inline_cb(Dwarf_Die *in_die, void *data)
                 pr_debug("found inline addr: 0x%jx\n",
                          (uintmax_t)pf->addr);
 
-                param->retval = convert_probe_point(in_die, pf);
+                param->retval = call_probe_finder(in_die, pf);
                 if (param->retval < 0)
                         return DWARF_CB_ABORT;
         }
@@ -1085,7 +1148,7 @@ static int probe_point_search_cb(Dwarf_Die *sp_die, void *data)
                         }
                         pf->addr += pp->offset;
                         /* TODO: Check the address in this function */
-                        param->retval = convert_probe_point(sp_die, pf);
+                        param->retval = call_probe_finder(sp_die, pf);
                 }
         } else {
                 struct dwarf_callback_param _param = {.data = (void *)pf,
@@ -1107,70 +1170,229 @@ static int find_probe_point_by_func(struct probe_finder *pf)
         return _param.retval;
 }
 
-/* Find probe_trace_events specified by perf_probe_event from debuginfo */
-int find_probe_trace_events(int fd, struct perf_probe_event *pev,
-                             struct probe_trace_event **tevs, int max_tevs)
+/* Find probe points from debuginfo */
+static int find_probes(int fd, struct probe_finder *pf)
 {
-        struct probe_finder pf = {.pev = pev, .max_tevs = max_tevs};
-        struct perf_probe_point *pp = &pev->point;
+        struct perf_probe_point *pp = &pf->pev->point;
         Dwarf_Off off, noff;
         size_t cuhl;
         Dwarf_Die *diep;
         Dwarf *dbg;
         int ret = 0;
 
-        pf.tevs = zalloc(sizeof(struct probe_trace_event) * max_tevs);
-        if (pf.tevs == NULL)
-                return -ENOMEM;
-        *tevs = pf.tevs;
-        pf.ntevs = 0;
-
         dbg = dwarf_begin(fd, DWARF_C_READ);
         if (!dbg) {
                 pr_warning("No dwarf info found in the vmlinux - "
                         "please rebuild with CONFIG_DEBUG_INFO=y.\n");
-                free(pf.tevs);
-                *tevs = NULL;
                 return -EBADF;
         }
 
 #if _ELFUTILS_PREREQ(0, 142)
         /* Get the call frame information from this dwarf */
-        pf.cfi = dwarf_getcfi(dbg);
+        pf->cfi = dwarf_getcfi(dbg);
 #endif
 
         off = 0;
-        line_list__init(&pf.lcache);
+        line_list__init(&pf->lcache);
         /* Loop on CUs (Compilation Unit) */
         while (!dwarf_nextcu(dbg, off, &noff, &cuhl, NULL, NULL, NULL) &&
                ret >= 0) {
                 /* Get the DIE(Debugging Information Entry) of this CU */
-                diep = dwarf_offdie(dbg, off + cuhl, &pf.cu_die);
+                diep = dwarf_offdie(dbg, off + cuhl, &pf->cu_die);
                 if (!diep)
                         continue;
 
                 /* Check if target file is included. */
                 if (pp->file)
-                        pf.fname = cu_find_realpath(&pf.cu_die, pp->file);
+                        pf->fname = cu_find_realpath(&pf->cu_die, pp->file);
                 else
-                        pf.fname = NULL;
+                        pf->fname = NULL;
 
-                if (!pp->file || pf.fname) {
+                if (!pp->file || pf->fname) {
                         if (pp->function)
-                                ret = find_probe_point_by_func(&pf);
+                                ret = find_probe_point_by_func(pf);
                         else if (pp->lazy_line)
-                                ret = find_probe_point_lazy(NULL, &pf);
+                                ret = find_probe_point_lazy(NULL, pf);
                         else {
-                                pf.lno = pp->line;
-                                ret = find_probe_point_by_line(&pf);
+                                pf->lno = pp->line;
+                                ret = find_probe_point_by_line(pf);
                         }
                 }
                 off = noff;
         }
-        line_list__free(&pf.lcache);
+        line_list__free(&pf->lcache);
         dwarf_end(dbg);
 
-        return (ret < 0) ? ret : pf.ntevs;
+        return ret;
+}
+
+/* Add a found probe point into trace event list */
+static int add_probe_trace_event(Dwarf_Die *sp_die, struct probe_finder *pf)
+{
+        struct trace_event_finder *tf =
+                        container_of(pf, struct trace_event_finder, pf);
+        struct probe_trace_event *tev;
+        int ret, i;
+
+        /* Check number of tevs */
+        if (tf->ntevs == tf->max_tevs) {
+                pr_warning("Too many( > %d) probe point found.\n",
+                           tf->max_tevs);
+                return -ERANGE;
+        }
+        tev = &tf->tevs[tf->ntevs++];
+
+        ret = convert_to_trace_point(sp_die, pf->addr, pf->pev->point.retprobe,
+                                     &tev->point);
+        if (ret < 0)
+                return ret;
+
+        pr_debug("Probe point found: %s+%lu\n", tev->point.symbol,
+                 tev->point.offset);
+
+        /* Find each argument */
+        tev->nargs = pf->pev->nargs;
+        tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
+        if (tev->args == NULL)
+                return -ENOMEM;
+        for (i = 0; i < pf->pev->nargs; i++) {
+                pf->pvar = &pf->pev->args[i];
+                pf->tvar = &tev->args[i];
+                ret = find_variable(sp_die, pf);
+                if (ret != 0)
+                        return ret;
+        }
+
+        return 0;
+}
+
+/* Find probe_trace_events specified by perf_probe_event from debuginfo */
+int find_probe_trace_events(int fd, struct perf_probe_event *pev,
+                            struct probe_trace_event **tevs, int max_tevs)
+{
+        struct trace_event_finder tf = {
+                        .pf = {.pev = pev, .callback = add_probe_trace_event},
+                        .max_tevs = max_tevs};
+        int ret;
+
+        /* Allocate result tevs array */
+        *tevs = zalloc(sizeof(struct probe_trace_event) * max_tevs);
+        if (*tevs == NULL)
+                return -ENOMEM;
+
+        tf.tevs = *tevs;
+        tf.ntevs = 0;
+
+        ret = find_probes(fd, &tf.pf);
+        if (ret < 0) {
+                free(*tevs);
+                *tevs = NULL;
+                return ret;
+        }
+
+        return (ret < 0) ? ret : tf.ntevs;
+}
+
+#define MAX_VAR_LEN 64
+
+/* Collect available variables in this scope */
+static int collect_variables_cb(Dwarf_Die *die_mem, void *data)
+{
+        struct available_var_finder *af = data;
+        struct variable_list *vl;
+        char buf[MAX_VAR_LEN];
+        int tag, ret;
+
+        vl = &af->vls[af->nvls - 1];
+
+        tag = dwarf_tag(die_mem);
+        if (tag == DW_TAG_formal_parameter ||
+            tag == DW_TAG_variable) {
+                ret = convert_variable_location(die_mem, af->pf.addr,
+                                                af->pf.fb_ops, NULL);
+                if (ret == 0) {
+                        ret = die_get_varname(die_mem, buf, MAX_VAR_LEN);
+                        if (ret > 0)
+                                strlist__add(vl->vars, buf);
+                }
+        }
+
+        if (dwarf_haspc(die_mem, af->pf.addr))
+                return DIE_FIND_CB_CONTINUE;
+        else
+                return DIE_FIND_CB_SIBLING;
+}
+
+/* Add a found vars into available variables list */
+static int add_available_vars(Dwarf_Die *sp_die, struct probe_finder *pf)
+{
+        struct available_var_finder *af =
+                        container_of(pf, struct available_var_finder, pf);
+        struct variable_list *vl;
+        Dwarf_Die die_mem;
+        int ret;
+
+        /* Check number of tevs */
+        if (af->nvls == af->max_vls) {
+                pr_warning("Too many( > %d) probe point found.\n", af->max_vls);
+                return -ERANGE;
+        }
+        vl = &af->vls[af->nvls++];
+
+        ret = convert_to_trace_point(sp_die, pf->addr, pf->pev->point.retprobe,
+                                     &vl->point);
+        if (ret < 0)
+                return ret;
+
+        pr_debug("Probe point found: %s+%lu\n", vl->point.symbol,
+                 vl->point.offset);
+
+        /* Find local variables */
+        vl->vars = strlist__new(true, NULL);
+        if (vl->vars == NULL)
+                return -ENOMEM;
+        die_find_child(sp_die, collect_variables_cb, (void *)af, &die_mem);
+
+        if (strlist__empty(vl->vars)) {
+                strlist__delete(vl->vars);
+                vl->vars = NULL;
+        }
+
+        return ret;
+}
+
+/* Find available variables at given probe point */
+int find_available_vars_at(int fd, struct perf_probe_event *pev,
+                           struct variable_list **vls, int max_vls)
+{
+        struct available_var_finder af = {
+                        .pf = {.pev = pev, .callback = add_available_vars},
+                        .max_vls = max_vls};
+        int ret;
+
+        /* Allocate result vls array */
+        *vls = zalloc(sizeof(struct variable_list) * max_vls);
+        if (*vls == NULL)
+                return -ENOMEM;
+
+        af.vls = *vls;
+        af.nvls = 0;
+
+        ret = find_probes(fd, &af.pf);
+        if (ret < 0) {
+                /* Free vlist for error */
+                while (af.nvls--) {
+                        if (af.vls[af.nvls].point.symbol)
+                                free(af.vls[af.nvls].point.symbol);
+                        if (af.vls[af.nvls].vars)
+                                strlist__delete(af.vls[af.nvls].vars);
+                }
+                free(af.vls);
+                *vls = NULL;
+                return ret;
+        }
+
+        return (ret < 0) ? ret : af.nvls;
 }
 
 /* Reverse search */